This invention relates to loop material, particularly to material to be engaged with hooking members to form a fastening, to its manufacture and use, and to fasteners comprising such loop material.
In the production of woven and non-woven materials, it is common to form the material as a continuous web that is subsequently spooled. In woven and knit loop materials, loop-forming filaments or yarns are included in the structure of a fabric to form upstanding loops for engaging hooks. As hook-and-loop fasteners find broader ranges of application, especially in inexpensive, disposable products, some forms of non-woven materials have been suggested to serve as a loop material to reduce the cost and weight of the loop product while providing adequate closure performance in terms of peel and shear strength. Nevertheless, cost of the loop component has remained a major factor limiting the extent of use of hook and loop fasteners.
To adequately perform as a loop component for touch fastening, the loops of the material must be exposed for engagement with mating hooks. Unfortunately, compression of loop material during packaging and spooling tends to flatten standing loops. In the case of diapers, for instance, it is desirable that the loops of the loop material provided for diaper closure not remain flattened after the diaper is unfolded and ready for use.
We have realized that non-woven fabrics constructed with certain structural features are capable of functioning well for their intended purpose as hook-engageable loop fabrics, while providing particular advantage in regard to expense of manufacture and other properties.
According to one aspect of the invention, a loop component of a hook and loop fastener is provided. The loop component has a nonwoven body of fibers with a basis weight of less than about 4 ounces per square yard (preferably, less than about 2 ounces per square yard). The fibers form a sheet-form base containing taut sections of fiber extending within a common plane between tightened knots of fibers, and a great multiplicity of loop formations dispersed across the base. Each loop formation has a trunk of fibers drawn together by taut fibers of the base and extending from an associated knot in the common plane of the base, and multiple hook-engageable loops formed of fibers of the trunk and extending from the trunk for engagement by hooks of a mating component.
In some embodiments, the majority of fibers forming the trunks and hook-engageable loops are crimped.
In some embodiments, the knots of the base each correspond to an associated previous penetration of the body of fibers by a needle. The body of fibers, in some such cases, may include crimped staple fibers.
In some loop components, the fibers comprising the trunks of the loop formations are secured together by a cured binder in interstices within the trunks. Preferably, the cured binder composes between about 20 and 40 percent of the total weight of the body of fibers.
In some cases, the fibers comprising the trunks of the loop formations are secured together by fused surface portions of at least some of the fibers comprising the trunks.
In some cases, the fibers comprising the trunks of the loop formations are secured together by interlocking crimps of the fibers.
In some embodiments, at least some of the fibers comprising the trunks of the loop formations each have a thickness that undulates along their length.
For some applications, the loop component also includes a resilient layer of foam laminated to the base of the body of fibers.
A layer of resin is, for some applications, laminated to the base of the body of fibers. The resin layer may form hook projections shaped to engage the loops of the component, for instance.
Preferably, the hook-engageable loops extend to an average loop height, measured as the perpendicular distance from the sheet-form base, of between about 0.020 and 0.060 inch, and the average loop height is between about 0.5 and 0.8 times the overall thickness of the body of fibers (defined to include the sheet-form base and a majority of the loops).
The sheet-form base has, in presently preferred embodiments, between about 50 and 1000 tightened knots per square inch of area, from which hook-engageable loop formations extend.
In some preferred configurations, the body of fibers is generally composed of fibers having a tenacity of at least 2.8 grams per denier.
For some important applications, the loop component preferably has a Gurley stiffness of less than about 300 milligrams.
By xe2x80x9chook-engageablexe2x80x9d and similar terms used above and throughout this specification, we mean that the loop material defines openings of size adequate to receive the tip or head portion of a male fastener element (such as a hook-shape or mushroom-shape element, for instance) for forming a fastening, and that the openings are exposed and extended for engagement.
By the word xe2x80x9centanglementsxe2x80x9d we mean that the nodes at which a multiplicity of fibers are intertwined in the non-woven web. These entanglements may be relatively loose, as formed directly by a needling process, for instance, or tightened after formation of the entanglements. By the word xe2x80x9cknotsxe2x80x9d we mean entanglements that have been tightened by applying tension to their intertwined fibers in at least one direction in the plane of the web, and remain in an at least partially tightened state.
By xe2x80x9cstabilizedxe2x80x9d, we mean that the web is processed to generally maintain its planar dimensions. In other words, a web xe2x80x9cstabilizedxe2x80x9d in a stretched condition will generally maintain its stretched dimensions and not significantly relax or stretch further under conditions of normal use. One way of xe2x80x9cstabilizingxe2x80x9d the web, for instance, is by solidifying binder at a significant proportion of its entanglements.
We have also realized that such loop fabrics as just described are advantageously produced by employing certain manufacturing techniques and methods.
According to another aspect of the invention, a method of forming a loop fastener component is provided. The method includes the steps of:
(1) providing a sheet-form mat of fibers;
(2) tensioning the base fiber by applying tension across the width of the mat, thereby forming a tensioned web; and
(3) stabilizing the web in its tensioned state.
The mat includes at least one base fiber of a length greater than the width of the mat and extending substantially across the mat, and loop fibers freely disposed within the mat. The tensioned web is formed by discrete, taut portions of base fiber extending between tightened entanglements. Relative movement between portions of the base fiber during tensioning draws together portions of the loop fibers to form upstanding, hook-engageable loops extending from the entanglements within the tensioned web. The stabilized web and loops have a combined weight of less than about 4 ounces per square yard. in some cases, the step of stabilizing includes solidifying a binder within the entanglements of the tensioned web.
Preferably, the step of tensioning increases the width of the mat by at least 20 percent.
In some embodiments, the step of providing a sheet-form mat of fibers includes continuously spinning the base fiber onto a supporting surface in a predetermined, overlapping pattern. In some cases, a pulsating air jet is impinged against the base fiber under conditions which cause the fiber to assumed a crimped form as it is spun.
In some embodiments, the base fiber has a cross-sectional property, such as thickness or cross-sectional area, that varies along its length.
According to another aspect of the invention, a method of forming a loop fastener component for hook-and-loop fastening includes stretching a generally planar non-woven batt of entangled fibers by at least 20 percent (preferably, at least 50 percent) in at least one direction in its plane, thereby producing a stretched web of weight less than about 4 ounces per square yard and having a generally planar web body with hook-engageable loops extending therefrom. A substantial number of fibers of the body are regionally taut in the plane of the web body as a result of the stretching, and extend in different directions radiating from bases of the loops. Afterwards, the web is stabilized in its stretched condition.
Preferably, the batt is retained against shrinking in a perpendicular direction within its plane during stretching.
In some embodiments, after stretching the batt in one direction the batt is stretched by at least 20% in another, perpendicular direction. In some other cases, the batt is simultaneously stretched by at least 20% in two perpendicular directions within the plane of the batt.
The stretching preferably causes the regionally taut fibers of the web body to be trained about loop-forming fibers in the bases of the loops, the batt being stretched in a manner that the loop-forming fibers form free-standing formations that extend from the plane of the web body, each formation containing multiple fibers and forming multiple, hook-engageable loops.
According to another aspect of the invention, a method of forming a loop fastener component for hook-and-loop fastening includes the steps of:
(1) providing a generally planar length of non-woven batt of entangled fibers, the batt having a thickness that varies across its width from one longitudinal edge thereof to an opposite longitudinal edge thereof;
(2) stretching the batt widthwise, thereby increasing the width of the batt by at least about 20 percent and producing a stretched web having a generally planar web body with hook-engageable loops extending therefrom (a substantial number of fibers of the body being regionally taut in the plane of the web body, and extending in different directions radiating from bases of the loops); and then
(3) stabilizing the web in its stretched condition. Advantageously, the stretching causes the thickness of the batt to become substantially uniform over its width.
Preferably, the stretched batt has weight less than about 4 ounces per square yard.
In some preferred embodiments, the stretched batt has width at least about twice the width of the batt prior to stretching.
The invention can provide a very inexpensive loop product which can very effectively engage and retain hooks, such as in hook-and-loop fasteners. The loop product can be particularly useful in combination with extremely small, inexpensive molded hooks as fasteners for disposable products, such as diapers, medical devices or packaging. We have found, for instance, that the structure of the extended xe2x80x9cloop treesxe2x80x9d of the material, described below in more detail, helps to prevent permanent flattening of the loops and provides some advantageous crush resistance.